Development of a Smart Modulator and Efficiency
Evaluation of 500 GeV e+e- C-band Linear Collider

An e+e- linear collider at 500-GeV c.m. has been proposed as a future
accelerator. The C-band linear collider has more than a thousand klystrons and
matching modulators. The linear colliders require smart modulators with high
reliability, compact and simple configuration, and good power efficiency. This study
suggests solutions to problems expected in the future linear colliders. A C-band
smart modulator has been developed using a constant-current inverter power supply.
The smart modulator provides 350-kV pulses of the pulse-to-pulse stability of 0.35%,
the pulse-width of 4.35 microseconds, and the repetition rate of 50 Hz. We also
investigated the power efficiency for the C-band scheme. A pulse efficiency of 75%
can be achieved by an optimized pulse transformer and the RF phase modulation. With
pulsed klystrons of 60% power efficiency, it is possible to achieve the RF system
efficiency of 32% with the wall-plug power of 170 MW.